1. Field of the Invention
The present invention relates to methods and apparatus for removing accumulated material deposits, e.g., film deposits, from processing chambers, and more particularly, to non-plasma in-situ cleaning of interior surfaces of semiconductor processing chambers.
2. Description of the Related Art
In the processing of a semiconductor wafer, to form integrated circuit structures therein, it is desirable to deposit materials including, for example, tungsten (W), titanium (Ti), tantalum (Ta), polysilicon, and/or silicon nitride on the wafer by a chemical vapor deposition (CVD) process. Chemical vapor deposition may occur by a conventional thermal CVD process, which involves supplying reactive gases to a substrate surface where heat induced chemical reactions (homogenous and heterogeneous) take place to produce a desired film. In the alternative, a plasma process may be implemented wherein a controlled plasma is formed to decompose and/or energize reactive species to produce the desired film.
Whether utilizing the thermal or plasma CVD process, thin films of deposited materials accumulate in the interior of the CVD deposition chamber. As a result, these thin film deposits must be removed periodically because they tend to affect the reproducibility of thin film deposition processes by changing the dimensions of the chamber. Also, the thin film deposits can flake off and contaminate the wafer being processed in the chamber.
In the current state of the art, it is conventional to remove such deposits using several different cleaning methods, including wet cleaning and in-situ cleaning.
The wet cleaning method necessitates the need for breaking the processing chamber""s vacuum seal and manually wiping down the chamber""s interior surfaces. Strong acid solutions are often used to dissolve the deposits on the interior surface of the chamber. Upon completion of the cleaning process, the chamber must be reassembled and resealed.
Inherent problems associated with this approach include the high volumes of hazardous chemicals that must be used in the cleaning process. Additionally, the manual breakdown of the processing system and subsequent reassembly is labor-intensive, time-consuming, increases wear on the processing chamber components, and may leave residual contamination within the chamber.
An in situ cleaning process is performed without disassembly of the process chamber. Typically, either plasma is generated for a dry etching process or a gaseous agent is flowed through the process chamber to remove accumulated films.
A plasma-enhanced cleaning process operates by introducing a continuous stream of gaseous fluorinated molecules, such as CF4, NF3, C2F6, C3F8, SF6 into a vacuum deposition chamber. A plasma is then ignited in the chamber during the gas flow, by connecting to a high frequency (radio or microwave) field. The increased energy creates atomic fluorine which promotes a reaction between the cleaning gas and any residue accumulated on the interior surfaces of the processing chamber.
While this process satisfactorily removes residues, the plasma physics require the continuous flow of large quantities of highly fluorinated gaseous molecules to maintain the plasma. In turn this generates highly reactive atomic radicals in the presence of the high frequency field. These reactive radicals lead to excessive amounts of extremely reactive and hazardous air pollutants, such as F2 and HF. Additionally, these plasma reactions are often only 40% efficient in the destruction of any perfluorinated compounds (PFC) gases that may form which are known to have a global warming potential (GWP) at least three times more powerful than CO2, and a lifetime of several thousands years in the atmosphere.
Another in situ method to remove residues from process chambers involves the introduction of a continuous flow of voluminous amounts of hazardous materials, such as HF or interhalogens, which also pose a significant risk to humans and the environment.
U.S. Pat. No. 4,498,953 describes an in-situ cleaning method in which an interhalogen, such as BrF5, BrF3, CIF3, or IF5 is continuously flowed through the processing chamber while maintaining a predetermined pressure within the chamber. At the end of the treatment, the flow of the interhalogen gas is terminated. However, a significant amount of hazardous material is moved through the system. Clearly, the high volume of material utilized in this method not only increases the cost of production but presents ancillary costs relating to the disposal of hazardous materials.
A similar problem exists in the process disclosed in U.S. Pat. No. 5,565,038 wherein a continuous flow of an interhalogen gas is introduced into a processing chamber to be used as a cleaning agent. Again, the flow of reactive gas is ongoing, and not terminated until the film removal is completed. Still further, as in the prior art cited above, this method is inherently problematic because of the large quantities of hazardous materials that are utilized, and the associated costs to the manufacturer and/or the environment. Additionally, the continuous flow cleaning process is performed under very low pressure and cleaning efficiency is reduced under such condition.
Other known methods for removing deposit buildup in processing chambers utilize NF3, including the types used in thermal CVD processes such as, vertical tubes. However, very high temperatures are required to crack NF3, to release the reactive fluorine ions. If these temperatures are not reached and/or maintained, hazardous NF3 is exhausted to the surrounding environment. In addition, the poor reaction selectivity of fluorine ions results in unwanted etching of the quartz reactor. Still further, depending on the shape of the processing chamber, uniform cleaning is not always predictable or accomplished.
Accordingly, it would be desirable to provide an improved cleaning process for deposit removal in a processing chamber, without the disadvantages of generating highly reactive radicals that may subsequently form perfluorinated greenhouse gases and/or using voluminous quantities of hazardous material thereby increasing production costs, disposal costs, and exposure risks to personnel.
It is a principal object of the present invention to provide an improved non-plasma cleaning method for removing deposits in a chemical vapor deposition chamber, utilized in either a plasma or thermal process, that reduces the volume of etching gas used in the cleaning method.
Another object of the present invention is to provide an improved non-plasma cleaning method that introduces a sufficient amount of an etching gas into a chemical vapor deposition chamber to effectively remove deposits therein with reduced production costs.
Still another object of the present invention is to provide an improved non-plasma cleaning method that does not generate unnecessary amounts of hazardous waste materials.
Yet another object of the present invention is to provide an improved non-plasma cleaning method that operates at higher pressures thereby increasing speed of the reaction rate.
A further object of the present invention is to provide an improved non-plasma cleaning method that operates at higher temperature thereby increasing the efficiency of the cleaning agent.
A still further object of the present invention is to provide an improved non-plasma cleaning method that uses reduced volumes of etching material but with increased utilization rates.
In one aspect, the present invention relates to a method for removing solid residue from interior surfaces of a processing chamber, by introducing a reactive substance into the interior of the processing chamber. The pressure is adjusted in the processing chamber to a predetermined level. When the pressure is adjusted, the introduction of the reactive substance into the processing chamber is terminated or substantially discontinued. The reactive substance is retained in the processing chamber for a sufficient time to react with the solid residue and form reaction products. The reaction products are subsequently removed from the processing chamber.
The non-plasma cleaning method disclosed herein may use any reactive substance that will react with the surface deposits to form a reaction product. Preferably, the reactive substance is a halogenated substance having at least one halogen substituent, e.g., F, Cl, Br, and I. The halogenated substance may be introduced into the interior of the processing chamber in an mount sufficient to increase the pressure in the vessel to a predetermined value, so that advantageously, no additional amount of the halogenated substance needs to be introduced into the processing chamber. As a result, the static method of the present invention provides unexpectedly superior results compared to continuous flow methods, and significantly reduces the amount of halogenated substance necessary for removing deposits within the processing chamber.
In another aspect, the present invention relates to a non-plasma cleaning process wherein internal pressures in the processing chamber are higher than those used in the prior art, thereby allowing a smaller amount of a halogenated substance to be more effective during the cleaning process while not reducing selectivity of the process.
The methods of the present invention may be used as an intermittent step or an in-situ step in an ongoing plasma etch process. Moreover, the cleaning methods can be employed with random non-disruptive frequency so as to prevent the accumulation of flaking residues that would otherwise inevitably result in contamination of the plasma etching process.
Accordingly, the present invention in one embodiment relates to a method for routinely controlling residue during CVD processing, either plasma or thermal, of a workpiece, comprising:
a) providing a processing apparatus including a processing chamber and a source of energy, either electrodes or thermal heat;
b) introducing a semiconductor workpiece into the processing chamber;
c) introducing a reactive gas into the processing chamber suitable for forming solid residues for deposition on the workpiece and interior surfaces of the processing chamber;
d) supplying energy in a sufficient amount to generate vapor deposition conditions;
e) removing the workpiece from the processing chamber; and
f) cleaning the interior surfaces of the processing chamber, comprising the steps of:
1) introducing into the interior of the processing chamber at least one halogenated substance capable of effectively reacting with the solid residue, the halogenated substance being in a sufficient amount to increase pressure within the processing chamber to a preset pressure level at a preset temperature; 2) discontinuing the flow of the halogenated substance into the interior of the processing chamber; 3) retaining the halogenated substance in the processing chamber for a sufficient time to effectively react with at least a portion of the solid residue to form at least one gaseous product; and 4) removing from the interior of the processing chamber the gaseous product and any remaining unreacted halogenated substance. Preferably, the preset temperature and pressure is maintained within the processing chamber during retention of the halogenated substance to increase the efficiency of the cleaning process.
In still another aspect, the present invention relates to applying the above described cleaning method wherein the halogenated substance is introduced into the chamber via a dispensing system that minimizes potential risks of leakage and/or malfunctioning regulator assemblies as disclosed in U.S. Pat. Nos. 6,101,816 and 6,089,027, and co-pending U.S. patent application Ser. No. 09/552,287 filed on Apr. 19, 2000, the disclosures of which hereby are incorporated herein by reference in their entirety.
In this regard, the present invention relates to a method of delivery of a reactive substance, in a gaseous phase, to the processing chamber from a fluid storage and gas dispensing system that provides additional safety measures for safe delivery of the reactive substance. Specifically, a method for fluid delivery of a gaseous reactive substance for cleaning a processing chamber comprises:
containing a reactive substance, in a fluid phase, in a confined state against at least one fluid pressure regulator in a fluid flow path closed to fluid flow downstream of the fluid pressure regulator, without flow control means between said fluid and said fluid pressure regulator;
selectively dispensing the confined fluid by opening the fluid flow path to fluid flow downstream of the fluid pressure regulator, and discharging fluid at a rate determined by the fluid pressure regulator; and
using the discharged fluid in the cleaning of a processing chamber.
The fluid delivery and gas dispensing system comprises:
a fluid storage and dispensing vessel enclosing an interior volume for holding a fluid, wherein the vessel includes a fluid flow port;
a fluid dispensing assembly coupled in fluid flow communication with the port;
at least one fluid pressure regulator associated with the port and arranged to maintain a predetermined pressure in the interior volume of the vessel;
the fluid dispensing assembly being selectively actuatable to flow gas, deriving from the fluid in the interior volume of the vessel, through the fluid pressure regulator and fluid dispensing assembly, for discharge of the gas from the vessel.
The fluid pressure regulator is preferably a double stage fluid pressure regulator system comprising two regulators, a high pressure stage regulator in contact with the liquid in the vessel and a low pressure stage regulator in fluid communication with the high pressure stage regulator. The double stage regulator system is preferred to reduce the possibility of leakage of contained fluid, e.g., internal liquids, particularly when the vessel is reposed on its side and the liquid inside exceeds a certain level. Fundamentally, the double stage regulator system provides a two-gate system, through which any fluid must pass before leakage can occur. If a small amount of fluid passes through the first gate, it will not be able to pass through the second gate because of the pressure difference, thereby preventing any unwanted leakage if the fluid storage and dispensing vessel is oriented in a horizontal position or otherwise tips over during its deployment.
Although the fluid pressure regulator, either a single or double stage system, may be positioned exteriorly, it is preferred that it is positioned interiorly in the fluid storage and dispensing vessel, so that it is protected by the vessel, e.g., cylinder casing or housing, from impact, environmental exposure and damage.
A still further aspect of the fluid dispensing system relates to the fluid storage and dispensing vessel discussed hereinabove containing a physical absorbent material having adsorbed thereon a gas at an internal pressure in the vessel, and a gas dispensing assembly coupled with the vessel and selectively operable to dispense gas from the vessel. The gas in the vessel may for example be at any suitable pressure, subatmospheric (e.g., 20-700 torr), atmospheric or superatmospheric (e.g., from about 50 psig to about 5000 psig).
The above and other aspects and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings.